The present invention relates generally to spoolable tubing suitable for use in the oil industry, and more particularly to spoolable tubing consisting of a composite material.
Spoolable tubing, that is tubing capable of being spooled upon a reel, is commonly used in numerous oil well operations. Typical oil well operations include running wire line cable down hole with well tools, working over wells by delivering various chemicals down hole, and performing operations on the interior surface of the drill hole. The tubes used are required to be spoolable so that the tube can be used in conjunction with one well and then transported on a reel to another well location. Steel coiled tubing is typically capable of being spooled because the steel used in the product exhibits high ductility (i.e. the ability to plastically deform). Unfortunately, the repeated spooling and use of steel coiled tubing causes fatigue damage that can suddenly cause the steel coiled tubing to fracture and fail. The hazards of operating steel coiled tubing, i.e. risk to personnel and high economic cost resulting from down time needed to retrieve the broken tubing sections, forces steel coiled tubing to be retired after a relatively few number of trips into a well.
Steel coiled tubing has also proven to be subject to expansion after repeated uses. Tube expansion results in reduced wall thickness with the associated reduction in the pressure carrying capability of the steel coiled tubing. Steel coiled tubing known in the art is typically limited to an internal pressure up to about 5,000 psi. Accordingly, higher pressure and continuous flexing typically reduces the steel tube""s integrity and service life.
For example, the present accepted industry standard for steel coiled tube is an A-606 type 4 modified HSLA steel with yield strengths ranging from 70 ksi to 80 ksi. The HSLA steel tubing typically undergoes bending, during the deployment and retrieval of the tubing, over radii significantly less than the minimum bending radii needed for the material to remain in an elastic state. The repeated bending of steel coiled tubing into and out of plastic deformation induces irreparable damage to the steel tube body leading to low-cycle fatigue failure.
Additionally, when steel coiled tubing is exposed to high internal pressures and bending loads, the isotropic steel is subjected to high triaxial stresses imposed by the added pressure and bending loads. The high triaxial stresses result in significant plastic deformation of the tube and diametral growth of the tube body, commonly referred to as xe2x80x9cballooningxe2x80x9d. When the steel coiled tube experiences ballooning, the average wall thickness of the tube is reduced, and often causes a bursting of the steel tube in the area of decreased thickness.
Steel coiled tubes also experience thinning of the tube walls due to the corrosive effect of materials used in the process of working over the well and due to materials located on the inner surface of the well bore. The thinning resulting from corrosive effects of various materials causes a decrease in the pressure and the tensile load rating of the steel coiled tubing.
It is, therefore, desirable to provide a non-steel coil tubing which is capable of being deployed and spooled under borehole conditions, which does not suffer from the limitations of steel tubing and is highly resistant to chemicals.
For the most part, prior art non-metallic tubular structures that are designed for being spooled and also for transporting fluids, are made as a hose whether or not they are called a hose. An example of such a hose is the Feucht structure in U.S. Pat. No. 3,856,052 which has longitudinal reinforcement in the side walls to permit a flexible hose to collapse preferentially in one plane. However, the structure is a classic hose with vulcanized polyester cord plies which are not capable of carrying compression loads or high external pressure loads. Hoses typically use an elastomer such as rubber to hold fiber together but do not use a high modulus plastic binder such as epoxy. Hoses are designed to bend and carry internal pressure but are not normally subjected to external pressure or high axial compression or tension loads.
When the ends of a hose are subjected to opposing forces, the hose is said to be under tension. The tensile stress at any particular cross-section of the hose is defined as the ratio of the force exerted on that section by opposing forces to the cross-sectional area of the hose. The stress is called a tensile stress, meaning that each portion pulls on the other.
With further reference to a hose subjected to opposing forces, the term strain refers to the relative change in dimensions or shape of the hose that is subjected to stress. For instance, when a hose is subjected to opposing forces, a hose whose natural length is L0 will elongate to a length L1=L0+Delta L, where Delta L is the change in the length of the hose caused by opposing forces. The tensile strain of the hose is then defined as the ration of Delta L to L0, i.e. the ratio of the increase in length to the natural length.
The stress required to produce a given strain depends on the nature of the material under stress. The ratio of stress to strain, or the stress per unit strain, is called an elastic modulus. The larger the elastic modulus, the greater the stress needed for a given strain.
For an elastomeric type material, such as used in hoses, the elongation at break is so high (typically greater than 400 percent) and the stress-strain response so highly nonlinear; it is common practice to define a modulus corresponding to a specified elongation. The modulus for an elastomeric material corresponding to 200 percent elongation typically ranges form 300 psi to 2000 psi. In comparison, the modulus of elasticity for typical plastic matrix material used in a composite tube is from 100,000 psi to 500,000 psi or greater, with representative strains to failure of from 2 percent to 10 percent. This large difference in modulus and strain to failure between rubber and plastics and thus between hoses and composite tubes is what permits a hose to be easily collapsed to an essentially flat condition under relatively low external pressure. This large difference also eliminates the hose""s capability to carry high axial tension or compression loads while the higher modulus characteristic of the plastic matrix material used in a composite tube is sufficiently stiff to transfer loads into the fibers and thus resist high external pressure and axial tension and compression without collapse.
The procedure to construct a composite tube to resist high external pressure and compressive loads involves using complex composite mechanics engineering principles to ensure that the tube has sufficient strength. It has not been previously considered feasible to build a truly composite tube capable of being bent to a relatively small diameter, and be capable of carrying internal pressure and high tension and compression loads in combination with high external pressure requirements. Specifically a hose will not sustain high compression and external pressure loads.
Moreover, the spoolable tubing commonly used in the industry does not attempt to identify the ambient conditions experienced by the spoolable tubing during oil well operations. These ambient conditions, such as temperature, pressure and axial strain can effect down hole operations.
Accordingly, it is one object of this invention to provide an apparatus for providing a substantially non-ferrous spoolable tube that does not suffer from the structural limitations of steel tubing and that is capable of being deployed and spooled under bore hole conditions.
Another object of the invention includes providing a coiled tubing capable of repeated spooling and bending without suffering fatigue sufficient to cause fracturing and failing of the coiled tube.
A further object of the invention is to provide a spoolable composite tube that identifies selected ambient conditions.
These and other objects will be apparent from the description that follows.
The invention attains the foregoing objects by providing a composite tubular member that offers the potential to exceed the performance limitations of isotropic metals currently used in forming coiled tubes and that senses the ambient conditions of the composite coiled tube. The composite tubular member is formed of a composite layer and pressure barrier layer that allows the composite tube to be repeatedly spooled and unspooled from a reel.
The composite tubular member, according to the invention, includes a substantially fluid impervious pressure barrier layer and a composite layer that together constitute a wall of the composite tube, an energy conductor embedded in the wall and extending along the length of the tube, and a sensor mounted with the wall. The composite layer is formed of a composite of fibers and matrix material. The sensor is connected with the energy conductor such that the sensor can communicate a signal by way of the energy conductor. The sensor responds to ambient conditions of the composite tubular member by communicating a signal on the energy conductor that is responsive to the ambient conditions
In one aspect of the invention, the sensor can be integrally formed with the energy conductor. Sensors integrally formed with the conductor are called intrinsic sensors.
Other aspects of the invention provide for different types of sensors for identifying various ambient conditions. The composite tubular member can include, individually or in combination: acoustic sensors, optical sensors, mechanical sensors, electrical sensors, fluidic sensors, pressure sensors, strain sensors, temperature sensors, and chemical sensors.
Optical sensors can be classified as interferometric sensors or as optical intensity sensor. Optical intensity sensors include light scattering sensors, spectral transmission sensors, radiative loss sensors, reflectance sensors, and modal change sensors. Another type of optical sensor is the Bragg grating sensor that can be disposed in a fiber optic cable.
Mechanical sensors include piezoelectric sensors, vibration sensors, position sensors, velocity sensors, strain sensors, and acceleration sensors. Electrical sensors includes sensors such as current sensors, voltages sensors, resistivity sensors, electric field sensors, and magnetic field sensors; and fluidic sensors include flow rate sensors, fluidic intensity sensors, and fluidic density sensors. Another type of sensor, the pressure sensor, includes absolute pressure sensors and differential pressure sensors. While temperature sensors include thermocouples, resistance thermometers, and optical pyrometers.
The sensors can be positioned throughout the composite tubular member. Preferably, the sensor is mounted with the wall formed by the composite layer and the pressure barrier layer. In particular, the sensor can be embedded in the composite layer or the pressure barrier layer, or sensor can be positioned between the pressure barrier layer and the composite layer. Additional aspects of the invention provide for mounting the sensor to the inner surface of the composite tubular member.
Further features of the invention include additional sensors that communicate signals by the energy conductor in the composite tubular member. The first sensor and any additional sensors can be distributed along the length of a single energy conductor, thereby forming a distributed sensor. These distributed sensors can communicate by way of the single energy conductor. In addition, the plurality of sensors forming the distributed sensor can be positioned at different locations along the composite tubular member.
Another feature of the invention includes a second energy conductor. In one embodiment, sensors can be connected in parallel between a first energy conductor and a second energy conductor. In another embodiment, the first sensor can be solely connected to the first energy conductor, while the second sensor can be only connected to the second energy conductor.
The energy conductors can be formed from various energy conducting medium, including hydraulic medium, pneumatic medium, electrical medium, and optical medium. The optical medium includes single-mode optical fiber, multimode optical fiber, and plastic optical fiber. Furthermore, the energy conductors can be embedded in the tubular member in various orientations. For instance, the energy conductor can extend helically along the length of the composite tubular member. Alternatively, the energy conductor can extend substantially axially along the length of the composite tube. In addition, multiple energy conductor can extend helically or axially along the length of the composite tube.
The composite tubular member can include other layers besides the pressure barrier layer and the composite layer. The composite member can include an interface layer to aid in the bonding between the pressure barrier layer and the composite layer. The composite member can include an inner protective layer or an outer protective layer. Additionally, the composite member can include an outer pressure barrier layer.
Various embodiments of the invention exist which include one or more of the layers described above. In one embodiment, the spoolable composite tube comprises an inner pressure barrier layer and an outer composite layer. In all embodiments, the tube can be designed to include or exclude an interface layer sandwiched between the inner pressure barrier layer and the composite layer. Other embodiments provide for a composite tube including an inner pressure barrier layer, a composite layer, and an outer pressure barrier. Further embodiments include an inner pressure barrier layer, a composite layer, an external pressure barrier, and an external protective layer. While in an additional embodiment, the composite tube might include only an inner pressure barrier layer, a composite layer, and an outer protective layer. A further aspect includes an inner protective layer, an inner pressure barrier layer, a composite layer, an external pressure barrier, and an external protective layer. The invention also contemplates a spoolable tube having an inner composite layer surrounded by the inner pressure barrier layer.
The composite tubular member, according to a further aspect of the invention, can include an interface disposed at an end of the composite tubular member. The interface is also connected with the energy conductor for coupling signals flowing along the energy conductor with external equipment. The external equipment can be a signal processor.
An additional embodiment of the invention provides for an interfacing apparatus for the composite spoolable tubular member. The interfacing apparatus includes a pressure sealing element, a load bearing element, and an energy coupler. The pressure sealing element is engagable with the spoolable tubular member for fluid communication with a fluid passage in the composite tubular member. The pressure sealing element maintains a pressure differential between the passage and ambient conditions. The load bearing element engages the spoolable tubular member and transfers a mechanical load between the spoolable tubular member and the interfacing apparatus. The energy coupler connects with at least one energy conductor of the spoolable tubular member for signal communication.
A further embodiment of the invention provides for a composite tubular member for spooling onto a reel and for unspooling for deployment, the composite tubular member comprising an inner protective layer, a substantially fluid impervious pressure barrier layer, and a composite layer formed of fibers and a matrix. The composite layer and the pressure barrier layer and the inner protective layer together constituting a wall of the tubular member.